and their security environment reflect that reality. but here in the u.s., there is a delicate balancing act between liberty and security. and it's still a work in progress. bret? >> bret: steve centanni live here in d.c. steve, thank you. some of the most compelling accounts to come out of boston are from the eyewitnesses. and the people who tried to help. correspondent douglas kennedy has that part of the story. [explosion] >> the bomb that where to through boilston street took with it lives and dreams. in fact, many people in boston and the nation. especially those who saw the mayhem firsthand. >> it went off, you know, my ears, you know, just from the compression of the explosive device hit us and shattered the window next to us. and, you know, and i looked back and i see a cloud of smoke. >> it took probably five or ten seconds to realize what had happened because it couldn't happen there. so, it was just too surreal. >> still personal tragedy quickly turned into communal hope as the city almost instantly came together. to comfort